MbsAux struct: Use the correct size for freeing variable associated to constraint (Ncons instead of nhu) (Issue #19)

Utilities dynamic lib

See merge request !19

User hardcoded

Based on the files used to generate the files "user_models" and "user_all_id", I extended them to generate the header file "user_hardcoded.h" where the values not changing during the simulation (gravity, mass, com positions, inertia, dpt) are saved as define macros with the floating value saved in the .mbs file.

This is potentially relevant for issue #20 : this generates the equivalent of this [file](https://gitlab.robotran.be/robotran/mbsysc/blob/06f1bdcb1f6c65a065a509fea80e8d9cde6a26c6/MBprojects/PendulumSpringC/symbolicR/mbs_dirdyna_hard_PendulumSpringC.h)

On top of that, I wrote a [python script](https://gitlab.robotran.be/robotran/mbsysc/blob/3018ff2250a332fa560cdc25a3dd495fde58820b/MBsysC/mbs_app/hardcoded_notation.py) able to transform a file generated by the current Robotran generator into the new format able to use these hardcoded values.

I tested it on my COMAN project (on dirdyna) and could not see any difference.

However, this is the first time I play with 'MDS_gen_strct* gen', so it could be fine if somebody could carefully look at the lines I implemented before merging this file.

@averle @fisette @TimotheeHabra @lantsoght

See merge request !13

Mbs dirdyn user

The field Mbsdirdyn is provided to the user through the file user_dirdyn.c

Pay attention that the user_dirdyn.c file generated with MBsysPad for a new project should be updated.

See merge request !18

Accelred

In this merge request, accelred in the generic files is implemented.

Pay attention that, as @fisette asked me, I changed all the 'qddu' of the project by 'udd'.

@averle @TimotheeHabra @lantsoght

See merge request !16

Visu viewpoint past

For real-time simulations, it is possible to go back in time with the keyboard.

However, changing the viewpoint after returning back in time will cause the visualization to return to the last multi-body system position (and not to the requested time in past).

This is solved in this branch.

See merge request !14